class Result {
    public:
        Result(bool isBST, int min, int max) {
            this->isBST = isBST;
            this->min = min;
            this->max = max;
        }
        bool isBST;
        int min;
        int max;
};

bool checkBST(Node* root) {
    if (root == NULL)
        return true;
    else
        return check(root)->isBST;
}

Result* check(Node* node) {
    int min = node->data;
    int max = node->data;

    if (node->left != NULL) {
        Result* leftResult = check(node->left);
        if (!leftResult->isBST || leftResult->max >= node->data)
            return new Result(false, 0, 0);
        min = leftResult->min;
        delete leftResult;
    }

    if (node->right != NULL) {
        Result* rightResult = check(node->right);
        if (!rightResult->isBST || rightResult->min <= node->data)
          return new Result(false, 0, 0);
        max = rightResult->max;
        delete rightResult;
    }
    return new Result(true, min, max);
}